A. Field of the Invention
The present invention relates to a new and improved device for gripping a workpiece during a rotary operation, and to a new improved method for quickly changing the gripping device to accommodate different operations and workpieces; and, more particularly, to a new and improved jaw assembly for a rotary chuck with a quick change top jaw and to a new and improved method for quickly attaching and removing a top jaw to and from a master jaw on a rotary chuck.
B. Description of the Background Art
Time is a critical, costly factor in the present manufacturing environment. During no previous period has awareness been keener that businesses live or die on their ability or inability to deliver the right number of manufactured goods to the right place at the right time. Few manufacturers, however, can afford to carry unlimited finished inventories in order to respond to unpredictable order cycles. This economic scenario accounts, in part, for the current trend toward shorter production runs.
To make shorter runs pay off, changeover and setup times must be cut to a minimum. This means jaw changes on chucks must be made in the shortest possible period of time. Today, however, estimates show that even an experienced operator with a complete set of top jaws including jaw nuts, keys and screws will require an average of twenty minutes to change a conventional set of jaws. Given a shop that normally performs three jaw changes per day, the sixty minutes of downtime means that twenty pieces will not be machined.
Presently, there are two basic quick-change designs for master and top jaws. In the first design the top jaw disengages from the master jaw and in the second design, the top and master jaws disengage from the chuck body as a single unit. Many of the designs include complicated structures that result in an expensive design. An example of one complicated design is provided in U.S. Pat. No. 3,219,356. Other designs use bolts to hold the top jaw to the master jaw as in U.S. Pat. No. 4,094,522. Although designs of this type allow easy change of the top jaws, the change is not quick. It is desirable to provide a chuck with a top jaw that may be changed quickly and easily and is not expensive to manufacture.